The green and orange spots are in the actual color spectre, and doesn't suddenly change. The text is what I've heard most positive about on dedicated graphics (Read: Signature) forums. Also, the grain is an effect.
I call it 'sudden' because they are only in a certain part of the signature; specifically the green.
The text, by my experience on 'signature forums', isn't the best I've seen. The font doesn't go with the 'smooth' style of the signature. And though the grain may be an effect, it doesn't help the signature in any way, and looks like random..
And some points I forgot to mention:
The lighting is wrong. If you look at your Tori, the lighting should be coming from the top right, (or the upper left of the Tori) rather than in the middle of the signature (the right of the Tori).
Also, the flow of the signature is non-existent; the abstract stuff behind the text has no prominent direction, the text goes to the lower right, the Tori goes to the upper right, the fire slightly to the lower right..
And finally, the focal point- it's all over the place. Try and utilize the blur and sharpen tools better.
*phew*